The present invention relates to road and rail tankers.
Tankers are widely used for transporting liquids and in the case of road transportation, numerous designs of tank have been produced to suit so called rigid chassis vehicles which are self powered and semi trailers which are pulled by a tractor unit, and drawbar trailers
The earliest designs comprised a single tank mounted on the chassis of a vehicle or trailer. Most tanks are formed with an integral longitudinal sub-chassis by which the tank is secured to the chassis of the vehicle or trailer. The typical vehicle chassis is of ladder construction and in practice is anything but rigid. Indeed it is intended to allow considerable flexing of the chassis, especially along its length, to accommodate variations in ground level.
When a tank is secured to a rigid vehicle chassis, the usual approach is to secure it positively using nuts and bolts connecting the chassis and the tank sub-chassis at several positions along its length. Usually a thin layer of rubber or felt is positioned between the respective chassis members to prevent rubbing due to metal to metal contact. This intermediate layer maybe of the order of 10 mm thick at most, often less, and offers little if any resilience.
As a consequence of the presence of the securely mounted tank the assembly is considerably stiffer than the chassis itself.
Most tanks are subdivided into a series of separate compartments each with their own inlet and outlet. This enables different liquids to be carried. For example in the case of fuels or lubricants, different grades of fuels or lubricants can be carried in the one vehicle.
However, these multi-compartment tanks are known to suffer from cracking of one or more of the internal dividing walls, even the outer walls of the tank shell. This results in contamination of the contents of one compartment with those of another and/or leakage of the contents. This needs to be avoided. The tanks have to be checked regularly to ensure integrity of each compartment. Gas pressurisation testing is the most reliable.
The cracking is believed to arise because of the repeated stressing of the tank due to the motion of the vehicle in use. Since the vehicle chassis or trailer chassis is less rigid than the tank any forces which cause twisting of the chassis will be transferred into the tank. However, the tanks are not able to resist these repeated twisting forces hence the above problem with cracking of the internal dividing walls and/or the external shell.
One attempt to try and solve this problem in the case of a rigid vehicle tank has been to mount the sub-chassis of the tank rigidly to the chassis of the vehicle at the rear of the chassis and to mount the other end of the tank chassis to the front of the vehicle chassis by way of over length bolts having coil springs applied about the shanks under the nuts to allow some movement of said end of the tank. This known arrangement allows approximately 25 mm of movement before coil binding but has not proved a solution to the problem. There is nothing against which the bolts can be tightened in this type of mounting.
It is believed that the flexing of a vehicle chassis or trailer can be in excess of 150 mm over the length of a typical chassis. Allowing for such a range of movement has not proved possible with the aforementioned proposals and consequently the problem of internal cracking remains.
The present invention aims to provide a solution.
Accordingly, a first aspect of the invention provides a road or rail tanker comprising a wheeled chassis and a plurality of tanks disposed in series one behind the other and wherein the plurality of tanks are individually mounted on the chassis each using a plurality of flexible mounts.
Each flexible mounting needs to allow at least upward and downward movement of the tank relative to a rest position so that twisting forces are not imparted directly to the tank. By using a plurality of tanks set along the length of the chassis, each tank mounting only has to be capable of accommodating a proportion of the total potential twisting movement of the chassis. A flexible mounting can be readily constructed to allow such amounts of movement while providing adequate support for the tank. The sort of amounting used for securing engines in the chassis of road vehicles can be readily adapted for this purpose. These allow movement in all directions relative to a rest position.
Each tank is able to move independently on its mountings and thereby accommodate the movement of the chassis at that location.
The tanks will be spaced apart in the longitudinal direction by an amount necessary to accommodate the permissible range of movement of each tank as the chassis twists and bends. As the movement of the chassis is not usually pure bending, but twisting, the tanks can be relatively close together than might otherwise be thought to be the case. The separation of the tanks is seen as aesthetically unpleasing and optionally the gap may be obscured by providing a continuity element. In one embodiment this is in the nature of a resilient plastic or rubber material, conveniently a length of flexible tube or piping, which at least extends down each side of the tanks at a position between the individual tanks. It is not necessary for the continuity element to be applied to the top or the base where it would not be visible to the casual observer. The gap between the tanks can provide a useful storage location for dip rods, air pipes, vents and wires. The continuity element may comprise a flat strip which is dimensioned to bridge the gap between the tanks and overlies the surface of the adjacent tanks. It may be secured to one of the tanks or be of a H-section to fit around respective end of flanges of the tanks. It may snap fit onto one of said flanges.
The preferred flexible mount comprises a resilient element made of rubber or the synthetic equivalent having a central bore receiving a metal sleeve. The resilient element is accommodated within a mounting flange to which it is secured by vulcanising, bonding or the like. The resilient element extends to both sides of the mounting flange. In use the mounting flange is interposed between flanges carried by the tank and the vehicle/trailer chassis such that a portion of the resilient element is under compression and a further portion projects through a hole in one of the flanges and is prevented from pulling through by a metal washer applied to the end thereof. A bolt passing through the assembly and carrying a nut to its other end secures the flexible mounting between the respective flanges of the chassis parts allowing relative movement of the tank with respect to the vehicle/trailer chassis. This construction allows the bolt to be fully tightened. It is preferred to provide at least 4 mountings for each tank. The number could be increased to carry heavier weights or individual mountings could be beefed up. Tanks that are at present made of steel to better withstand the imposition of bending and twisting forces could now be made of light alloys, such as aluminium. The reduction in weight will enable the tanks to be larger, thereby permitting increased quantities of liquid to be carried without increasing the overall vehicle/trailer gross weight.
The wheeled chassis may be a four, six or eight wheeled rigid self powered road vehicle, or a draw bar trailer, or an articulated semi-trailer for the road. There are advantages in the case of a semi trailer if the chassis, when connected to the tractor unit, can slope downwardly to the wheels of the trailer. For example it permits greater vertical articulation, i.e. downward movement of the trailer unit with respect to the trailer. However, such a construction when used with conventional multi-compartment tankers of the type where each compartment has to have a calibrated dip rod has problems as the inclination will result in a lack of horizontal symmetry and consequently the dip rod readings will be inclination dependent. However, this problem can be overcome when a plurality of separate tanks are used as each can be constructed so as to maintain symmetry and will have a volumetric centre line as discussed hereinafter. Accordingly it is proposed that the bottoms, and preferably also the tops, of the plurality of tanks are substantially horizontal when the trailer is connected to the tractor. Furthermore, it is proposed that the plurality of tanks disposed in line one after the other have an increasing depth in a direction from the front to the rear of the trailer. In practice this will result in the bottoms of adjacent tanks being relatively stepped in order to maintain horizontal symmetry of the tanks as discussed further hereinafter. It is preferred to mount each of the tanks using a plurality of flexible mounts in accordance with the earlier proposals. At least four mounts are provided. The forward mountings which connect the respective tanks to the chassis will be shorter than the rear flexible mountings in order to maintain the desired alignment.
It is a requirement of trading standards that each compartment of a tank has its own unique calibration chart and that each compartment is provided with a dip rod which is calibrated according to the respective calibration chart. A tanker builder is required to provide facilities for dipping each tank and the dip rod has to be located at the volumetric centre of the tank. The volumetric centre is the position in the tank at which the liquid therein never alters its height irrespective of the angle of inclination of the tank, at least within the limits of accuracy demanded by the trading standards. Tanks are generally constructed symmetrically such that this position when assessed in any horizontal plane defines a vertical axis. However, these dip tubes cannot be used for tanks containing petrol because the current regulations do not allow petrol vapour to enter the atmosphere. Most deliveries of petrol utilise a so called gravity drop which is not metered. Accordingly, there is currently no means for the quantity of petrol being delivered to be checked. The customer has to rely on unofficial metered readings of the quantity of fuel which has been loaded at the depot.
A solution is described herein. When multiple tanks are used as proposed in the above-described aspect of the present invention, it becomes possible and practical to use a sight tube to determine the quantity of liquid in each compartment. Whilst each tank preferably comprises a single compartment, sight gauges may be used with multiple compartment tanks. If the outlet of the sight tube is disposed on the longitudinal centre line of the tank sideways inclination of the tank will unaffect the reading on the sight gauge.
If the tanker is standing level, as viewed longitudinally, when the reading is taken a single sight gauge will suffice. If it is out of level the reading will need to compensate for the degree of out of level. Means may be provided for measuring the angle of inclination and, a correction factor applied as appropriate for a particular tank.
Inclination in the longitudinal direction can be catered for by utilising two sight gauges for each tank, one at each end. The average of the opposite end readings will determine the quantity of liquid in the tank. The longitudinal inclination will usually be small such that averaging of the readings gives a sufficiently accurate value.
In the case of a multi-compartment tank the sight gauges are placed at any convenient end of the tank containing the multiple compartments and may be confined to a single sight gauge for each compartment. The compartments are numbered and the sight gauge for each compartment is identified by the same number.
The gauges are officially calibrated when the tank is level.
The sight gauges are vented back into the tank to avoid spillage as well as to avoid air locks and to prevent vapour entering the atmosphere. The location of the sight gauges between the tanks lessens the likelihood of damage. The end most sight gauges can be shielded to lessen the likelihood of damage. A valve is conveniently provided at or adjacent the connection of the sight gauge with the tank. This valve can be manually or remotely operable. It can be an air or electronically operated valve. Its operation may be linked to operation of the tanker discharge valves or operated independently.
A second aspect of the invention provides apparatus for measuring the quantity of liquid in a road/rail transport tank comprising a pair of sight gauges centrally disposed at opposite ends of said tank and fed from a common or a respective outlet disposed on the longitudinal centre line of the tank, and a calibration for each sight gauge.
The sight gauges extend upwardly a sufficient distance to be able to show that the tank is full when the tank is longitudinally inclined taking into account the ullage. Preferably the upper end of the sight gauge is vented into the tank.
A third aspect of the invention provides a method of measuring the quantity of liquid in a road/rail transport tank utilising a pair of calibrated gauges as aforesaid, the method comprising averaging the readings of the two gauges.
The sight gauges branch from the tank and are vented back into the tank. Furthermore, the liquid in the sight gauge is the liquid contained in the tank.
The configuration of the tanks can give rise to problems with the accuracy of the readings with the second and third aspects of the invention and further aspects of the invention disclosed further hereinafter aim to address these problems.
In building mobile tankers for transporting liquids it is recognised that it is undesirable to utilise planar walls for the tanks because these are less able to withstand impact forces applied to them by movement of the liquid within or otherwise. As a consequence it is common for side walls to have a swept configuration (2D curvature) and for end walls to be either dished (3D curvature) or swept (2D curvature). Quite often the rear end wall and the front end wall are convexly curved (as viewed externally).
In deciding to split a large single compartment or multi-compartment tank into a series of separate tanks disposed in line one behind the other, I initially opted for each tank to have a concavely swept end and a convexly swept end. This is advantageous as it allows the nesting of adjacent tanks thereby reducing the dead space between the adjacent tanks whilst ensuring that each of the tanks benefit from the strength advantages o f swept ends.
For most practical purposes each tank can be regarded as having opposite end walls, opposite side walls and top and bottom walls. More particularly, the opposite end walls will be curved for constructional reasons as mentioned above. Most usually the opposite side walls and the top and bottom walls will also be curved, and preferably, the tank shell will have a cross-section which is of so called max section, or which is elliptical or round (as viewed in vertical section).
Accordingly a fourth aspect of the invention provides a tanker comprising a plurality of tanks disposed in a line one behind the other, and wherein opposite end walls of each tank are curved and wherein the adjacent end walls of two adjacent tanks are complimentarily curved.
This aspect may be applied to any of the other aspects described herein.
In one embodiment the opposite end walls of each tank are correspondingly curved, whilst in another embodiment the opposite end walls of each tank are complimentarily curved.
However, in adopting my proposal for the use of sight gauges to measure the quantity of liquid in such tanks, problems can arise with the ability to position the sight gauges correctly in order to give the desired accuracy of the reading when the tank is off level. Thus, a configuration of tank is required that will allow close nesting of the plurality of tanks and that will allow convenient positioning of the sight gauges to give a sufficiently accurate reading. Another aspect of the invention aims to provide an advantageous solution.
Accordingly, where a pair of sight gauges are to be used to measure the quantity of liquid in the tank it is preferred that the ends of each tank are correspondingly curved. This ensures that the pair of sight gauges can each be positioned in close proximity to the respective ends of the tank in question and located on a diameter at equal distances from the volumetric centre line.
It is necessary in order to be able to measure the quantity of liquid in the tank sufficiently accurately to satisfy trading standards, that the tank, when viewed in any horizontal section has a vertical axis line which represents the volumetric centre of the tank. For convenience this axis is referred to as the volumetric centre line, and as mentioned above this should correspond to the position that the dip rod would be located. A tank having symmetry about this axis is referred to as an horizontally symmetric tank. With such a construction the reading from a pair of sight gauges placed on a diameter at equal distances on opposite sides of the volumetric centre line when averaged will give a sufficiently accurate reading to satisfy trading standards irrespective of any displacement of the tank from the horizontal. Currently trading standards seek an accuracy of 0.5% for the volumetric capacity reading. Accordingly, when we talk about a tank having horizontal symmetry, it only has to be symmetric to an extent to provide a sufficiently accurate reading to satisfy trading standard requirements. Furthermore, the range within which volumetric readings can be relied upon can be specified and need not require the whole of the tank from the bottom upwards to be volumetrically symmetric. Thus symmetry may start at a minimum volume thereby allowing the lower portion of the tank to be non-symmetric. The reference to horizontally symmetric as used herein is to be understood not to be limited to horizontal symmetry from the bottom of the tank but may be from any specified minimum volume for measurement purposes and may also accommodate variations from horizontal symmetry which produce a sufficiently accurate reading. The sight gauges can be disposed on any diameter, not merely on the longitudinal centre line of the tank. However, in order that the pair of sight gauges can be placed in close proximity to the opposite ends of the tank the opposite end walls of the tank will also lie at equal distances from the volumetric centre line when viewed on any horizontal diameter passing through that centre line.
Accordingly a fifth aspect of the invention provides a tank which is horizontally symmetric about a volumetric centre line, and which comprises a pair of sight gauges disposed parallel to said volumetric centre line and set at equal distances on a diameter centred on said volumetric centre line.
A sixth aspect of the invention provides a method of measuring the quantity of liquid in a tank which is horizontally symmetric about a volumetric centre line, and in which the tank further comprises a pair of calibrated sight gauges disposed parallel to said volumetric centre line and set at equal distances on a diameter centred on said volumetric centre line, in which method the readings from the pair of sight gauges are averaged to determine the quantity of liquid in the tank. The sight gauges branch from the tank and are vented back into the tank.
Furthermore, the liquid in the sight gauge is the liquid contained in the tank. A calibration is provided for each sight gauge.
It is a requirement that a vapour recovery system is provided for the tanks to avoid petrol vapour entering the atmosphere and another aspect of the invention aims to provide an advantageous vapour recovery system which in the case of a tanker comprising a plurality of flexibly mounted tanks allows movement of the tanks, and in the case of tanks that are horizontally symmetric does not compromise the readings from a sight gauge or gauges.
Accordingly a seventh aspect of the invention provides a vapour recovery system for a tank which is horizontally symmetric about a volumetric centre line, the tank further comprising a pair of members disposed within the tank substantially parallel to said volumetric centre line and set at equal distances on a diameter centred on said volumetric centre line, and in which one of the members serves as a vent pipe and emerges from the tank and communicates with a manifold which has provisions for connecting to a vapour recovery tank.
If the members are off vertical, any change to the symmetry is only small and in any event will give a more accurate reading than a single pipe. The other member comprises a matched pipe which may carry services such as air and/or electric services. Usually the members will be hollow members extending through the tank from the top to the bottom.
This aspect may be applied to any of the other aspects described herein.
In the case of a tanker comprising a plurality of tanks, especially flexibly mounted tanks as aforedescribed, the manifold may comprise a plurality of sections corresponding in number to the number of tanks and with each section connected by a flexible connection. In an alternative a single manifold is provided and the respective vent pipes connect with the manifold by way of a respective flexible joint. Preferably, the vent pipe emerges at or adjacent the bottom of the tank and extends through the tank to emerge at the top of the tank and to be connected back in to the top of the tank via a valve.
A single sight gauge can also give a sufficiently accurate reading in conjunction with a level measuring device which is set on a line extending between the sight gauge and the volumetric centre line when the level gives a level reading. Again the line can be on any diameter. This is particularly useful with multi-compartment tanks or where one of the pair of sight gauges cannot be used because its position would interfere with an adjacent tank.
Accordingly an eighth aspect of the invention provides a tank for liquid which comprises a sight gauge which branches from the tank and which is vented back in to the tank and further comprising a level measuring device.
A ninth aspect of the invention provides a method of measuring the quantity of liquid in a tank, the tank having a calibrated sight gauge and a level measuring device, the method comprising checking the level measuring device to check that the tank is level and reading off the quantity of liquid in the tank from the calibrated gauge.
In one embodiment the tank is horizontally symmetric about a volumetric centre line and the sight gauge is disposed parallel to said volumetric centre line and the level measuring device set on a horizontal diameter aligned with said volumetric centre line and said sight gauge. Accordingly the method comprises checking that the level reads level along said line. A simple linear bubble level may be used for the level measuring device. Any other means that would indicate the degree of level, such as a digital level gauge, may be used. In another embodiment which does not require the tank to be horizontally symmetric, the level measuring device is configured to be able to indicate when the tank and hence any liquid in the tank is level, i.e. horizontal. A bubble level may be used of the type that comprises a circular chamber. Alternatively a T level may be used or any other level measuring device which would have the same effect.